Task listener specified by class - CDI

Camunda 7 Topics Discussion & Questions
1

Hello,

I am trying to create a task listener which would notify all candidate users about creation of the task. However, dependency injection is not working for me.

The task listener is define as following:
<camunda:taskListener class="poc.ReferentListener" event="create" />

The ReferentListener class implements TaskListener interface:

@Named(value = "ReferentListener")
public class ReferentListener implements TaskListener {

    @Inject
    private IdentityService identityService;

    @Override
    public void notify(DelegateTask delegateTask) {
        ...
    }

    public void test() {
        System.out.println(identityService);
    }
}

notify(DelegateTask) method is called correctly, when the create-event occurs. But NullPointerException is thrown, when using IdentityService.

I tried to substitute the tasklistener definition with this:
<camunda:taskListener expression="${ReferentListener.test()}" event="create" />
then identityService was correctly instantiated.

–

Slightly offtopic: Is this the best practice? Or is there more suitable solution?

2

Probably because when using class the instance is created as a POJO with the new keyword, not by the IoC/bean container.

The docs state expressions must be used for injection. Delegation Code | docs.camunda.org

To inject values that are dynamically resolved at runtime, expressions can be used. Those expressions can use process variables, CDI or Spring beans.

3

Hi,

The answer from @nvanbelle is correct.

Cheers,
Christian

4

Thank you guys for your advice! That did the work.

5

An addition: You can use the process engine configuration class org.camunda.bpm.engine.cdi.CdiStandaloneProcessEngineConfiguration. This configuration uses an artifact factory (that is called when the engine instantiates classes), that looks into the application’s CDI context.

Cheers,
Thorben

1 Like
6

I just had another look at the code. Should also work for shared engines. I thought we would cache the resolved class but that is not the case. I’ll update before answer.

7

Hi thorben. There is some example on how to configure the default shared engine for this kind of purpose ?

Using a delegateExpression with a bean could be a solution but the field injection is permanent (as it’s a singleton bean) and I can use custom spring beans already wired.
Using a Class is a better solution because my injected fields are changing every time, but inside that class actually I can’t inject useful bean like db connections, custom services etc, and I don’t want to specify those beans for every call.

For example for a TaskListener : class : pack.CompleteTask
injected field : var1 (manually set on modeler)
injected field : var 2 (manually set on modeler)
Inside the notify method of CompleteTask class:
bean1.foo(var1, var2, task.getExecution().getVariable(“form_var_foo”))
bean2.bar(var1, var2)

I want var1,var2 to be specified every time, while bean1 and bean2 should be autowired at every class instantiation. Is this possible ? Or there is a way to detect spring environment from this class and get the desired beans ?

8